1. Field of the Invention
The invention relates to a method and a device for the introduction of fuel into a premixing burner, with a pilot gas feed and a premix gas feed for the operation of a gas turbine for the entire load range, the pilot gas feed being carried out via a burner lance provided in the premixing burner and the premix gas feed being carried out via side wall shells of the premixing burner.
2. Brief Description of the Related Art
Premixing burners for the operation of gas turbine plants are operated in a way known per se with different fuel feed systems, so that the entire load range of a gas turbine can be covered, that is to say from the ignition and starting phase up to the full-load range of the gas turbine. Thus, during starting and also in lower load ranges of gas turbines, premixing burners are supplied with pilot gas which is fed usually via a central burner lance into the interior of the premixing burner. After the start and run-up of the combustion operation have taken place within the premixing burner, there is a pilot/premix changeover, in which, to raise the burner capacity and a consequently necessary increased supply of fuel, premix gas flows into the interior of the premixing burner through hole ducts which are provided inside the burner shells enclosing the premixing burner. During the changeover to premix operation, however, high pulsations occur, with the effect of oscillating pressure fluctuations which markedly reduce the useful life of the combustion chamber following the premixing burner and of the downstream gas turbine. Even in the event of mixed operation, that is to say a simultaneous feed of pilot gas and premix gas into the interior of the premixing burner, only unsatisfactory combustion results are obtained, especially since the pilot gas addition maintained during the premix gas feed considerably disturbs the vortex core of the combustion air flowing into the premixing burner. A satisfactory coordination between the pilot gas supply and the premix gas supply is not possible by means of the conventional arrangements.
In order nevertheless to achieve acceptable combustion qualities, particularly in the low load range, the burner lance, which projects into the interior of the premixing burner and via which a pilot gas feed takes place, is designed in such a way that, under low loads, the combustion operation is run solely via the pilot gas supply, the premix stage remaining inoperative. In order to make such an operating mode possible, however, it is necessary for the selected line cross section of the burner lance to be correspondingly large, so that a pilot gas supply can be made available to the premixing burner to a sufficient extent even for the lower load range. Burner lances with such a large line cross section are not suitable for mixed operation, however, since this gives rise to an increased extent to the above-described irritation in the inflowing combustion air and may generate undesirable combustion chamber pulsations in an intensifying way.